It is now well known to reduce or eliminate shock hazard by providing electrical tools and appliances with three-wire power cords terminating in three-prong plugs adapted to be plugged into three-wire grounded receptacles.
Such three-prong plugs have two power prongs, which correspond generally in structure and function to the prongs of the plugs used in connection with conventional two-wire electrical systems, and a third or grounding prong adapted to engage the grounded female contacts of three-wire grounded receptacles.
Unfortunately, many electrical receptacles commonly found in homes and other buildings are of the two-wire ungrounded variety, rather than the three-wire grounded variety. That is to say, many electrical receptacles commonly found in use today are not provided with a third female contact and corresponding opening adapted to interfit with the grounding prong of a three-prong plug. Adapters are often used to make it possible to use the three-prong plugs with conventional two-wire receptacles but many times such an adapter cannot be found when needed.
This problem is commonly resolved by cutting off the grounding prong of a three-prong plug, thus making it possible to plug the three-prong plug into a two-wire receptacle, but at the same time "accepting" the attendant shock hazard of an ungrounded system. After being thus mutilated the three-prong plug can still be plugged into a three-wire receptacle, but cannot be used to take advantage of the shock protection offered by the ground connection of the three-wire receptacle.
Another known method of dealing with this problem is to mount the grounding prong of a three-prong plug on a pivot, so that if the grounding prong is not to be used it can easily be swung to an inoperative position. This method is not entirely satisfactory because of the poor electrical conducting properties of the simple type of pivot which is generally used. Further, such pivots are subject to wear and corrosion, and thus the user of a particular tool or appliance equipped with such a pivotable prong plug may be relying upon a faulty ground connection, and thus be unprotected from electrical shock, when he believes he is protected.
These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.